Aftermarket vehicle security systems and aftermarket vehicle control systems must be capable of operating in a variety of different vehicle makes and models. To achieve full operational performance, an aftermarket system must be capable of controlling specific electrical accessory functions. For example, power door lock operation is one electrical accessory function which is controlled by many aftermarket systems. To date, primarily two electrical power door lock designs have been utilized.
A single voltage level input signal may be used to control the operation of electrical accessory circuits. For example, a power door lock circuit would comprise one lock input wire and one unlock input wire from each door lock switch. When the door lock switch is moved to the lock position, a battery voltage control signal is transmitted via the lock input wire. When the door lock switch is moved to the unlock position, a battery voltage control signal is transmitted via the unlock input wire. To interface with this type of electrical environment, many aftermarket systems are designed to produce battery voltage control signals. These aftermarket systems produce the battery voltage control signal either by supplying a battery voltage or a ground to the appropriate circuit.
A multiple voltage level input signal may also be used to control the operation of electrical accessory circuits. In this design, control signals are multiplexed, i.e. multiple voltage levels are communicated on a single wire, and therefore a lesser number of input wires is required. For example, a multiplexed power door lock circuit may contain only one input signal wire from each door lock switch. When the door lock switch is moved to the unlock position, a 12 volt signal is transmitted via the input wire. When the door lock switch is moved to the lock position, a 6 volt signal is transmitted via that same single input wire.
In comparing the two designs, the multiplexed design has multiple control voltage levels transmitted via a single wire, while the non-multiplexed design has a single control voltage level which must be transmitted via multiple wires.
The multiplexing of electrical accessory circuits has created difficulties in adapting aftermarket systems to vehicles using a multiplexed design. Many present aftermarket systems produce only single voltage level outputs, however multiple voltage level control signals are required to operate multiplexed vehicle accessory circuits.
Currently, retrofitted wire harnesses have been used to adapt aftermarket systems to specific vehicle makes and models. The disadvantages of this practice are numerous. For example, this practice complicates the installation process, reduces production efficiency and quality, increases the number of required stock parts, and increases inventory costs.